Density dependent and temporal variability in habitat selection by a large herbivore; an experimental approach

Both density dependent and density independent processes such as climate affect population dynamics in large herbivores. Understanding herbivore foraging patterns is essential to identify the underlying mechanisms behind variation in vital rates. However, very little is known about how animals vary their selection of habitat temporally, alone or in interaction with density during summer. At the foraging scale, we tested using a fully replicated experiment whether domestic sheep Ovis aries stocked at high (80  per  km²) and low (25  per  km²) densities (spatial contrasts) varied their habitat selection temporally over a four year period. We predicted reduced selection of high productivity vegetation types with increasing density, and that seasonal and annual variation in climate would affect this density dependent selection pattern by increasing competition for high quality habitats in late grazing season and in years with poor vegetation development and over time related to vegetation responses to grazing. As predicted from the Ideal free distribution model, selection of high productivity habitat decreased at high density. There was also a marked temporal variation in habitat selection. Selection of the most productive vegetation types declined towards the end of each grazing season, but increased over years both at low and high sheep density. There was only weak evidence for interactions, as selection ratio of highly productive habitats tended to increase more over years at low density as compared to high density. Limited interactive effects of density and annual variation on habitat selection during summer may explain why similar interactions in vital rates have rarely been reported for summer seasons. Our results are consistent with the view that variation in habitat selection is a central mechanism for climate and density related variation in vital rates.     

Formation of guanosine 3′,5′-cyclic monophosphate by thyroliberlin in cultured rat pituitary cells a possible role in stimulation of prolactin synthesis

In a clonal strain of rat pituitary tumour cells (GH₄C₁ cells), thyroliberin stimulated prolactin secretion and synthesis: effects that could be demonstrated after 5 min and 4–5 h of treatment, respectively. Within 0.5–5 min after addition of thyroliberin, maximal increases (2–4 hold) in cellular cyclic GMP concentrations were observed, and this rise preceded or occurred simultaneously with that of cyclic AMP. After 60 min of treatment the concentrations of the cyclic nucleotides had returned to control values. Half maximal and maximal stimulation of cyclic GMP elevations were obtained with approx. 2·10⁹ and approx. 27·10^?9 thyroliberin, respectively. Aminophylline increased both cyclic GMP and cyclic AMP, and potentiated the stimulatory effects of thyroliberin on both cyclic nucleotides. The dibutyryl derivative of cyclic GMP (10^?4–10^?6 M) stimulated prolactin synthesis, but not hormone release. Prostaglandin E₂ (3·10^?7 M) stimulated cellular cyclic AMP concentrations, but did not affect cyclic GMP levels. We conclude that thyroliberin in the GH₄C₁ ccell strain stimulates cyclic GMP formation, in addition to elevate cyclic AMP concentrations. The stimulatory effect on cyclic GMP is probably not secondary to the rise in cyclic AMP concentration, since prostaglandin E₂ elevates only cyclic GMP is involved in the action of thyroliberin on prolactin, the present results suggest a role on hormone synthesis.     

Individual Heterogeneity in Use of Human Shields by Mountain Nyala

The ‘human shield hypothesis’ describes the situation where prey species use humans as shield from natural predation. We tested the human shield hypothesis in a population of mountain nyala (Tragelaphus buxtoni) subjected to predation from the nocturnal spotted hyena (Crocuta Crocuta) in the Bale Mountains National Park, Ethiopia by radio‐marking 15 mountain nyala (seven females and eight males) and tracking them for up to 2 yr. Occurrence of hyena estimated by faecal transects decreased close to human settlements substantiating the occurrence of a zone with lower risk of hyena predation. The diurnal pattern in the average distance between mountain nyala relocations and human settlements was consistent with the human shield hypothesis with significantly shorter distances during night (when exposed to predation) than during day. However, mountain nyala showed large individual heterogeneity in use of human shields. While nearly all individuals occasionally moved out of the park to human settlements during night, the frequency of such excursions varied from 0% to 71%. The excursions occurred year‐round and were not driven by seasonal access to crops. We have previously demonstrated a strong negative effect of humans on the large‐scale distribution pattern of mountain nyala. The use of human shield documented here is indicative of a positive small‐scale effect of humans. Our study thus supports the view that the effect of human–wildlife interactions can be scale‐dependent.     

The effect of agricultural land use practice on habitat selection of red deer

The population of red deer (Cervus elaphus) has increased substantially in many western European countries during recent decades. Simultaneously, agricultural practices have undergone major changes. Observations suggest that meadows and pastures are important sources of nutrients for deer, but there are few studies quantifying the selection of agricultural land by deer in general. Here, we study red deer selection of various types of agricultural land and the history of land use (times of fertilisation and since renewal) in Norway. We used data from 14 female and 12 male red deer with GPS collars during the years 2007–2010. Our study design was to compare pairs of agricultural fields that had received “low” and “high” use by a given individual red deer and data were analysed by using case–control logistic regression. Our results showed that both sexes selected meadows over other types of agricultural land. Females selected intensively fertilised meadows and meadows of intermediate age, while male selection did not depend on meadow age (time since renewal) or fertilisation. The smaller females thus selected meadows of high quality, while the larger males continued to use old meadows of lower quality but rich in biomass. Our analysis suggests that a decreasing supply of meadows in the future due to lower production of livestock fodder may also affect management of red deer, and that a future change in the intensity of agricultural practices may affect sexes of wild large herbivores differently.     

Maximal oxygen deficit of sprint and middle distance runners

Anaerobic energy capacity was evaluated by maximal oxygen deficit (MOD) as well as by blood gas and muscle biopsy variables during short exhausting running in six recreational (RR) and eight competitive sprint and middle distance runners (SMDR). On 3 days runs to exhaustion were executed. Two runs were performed at a treadmill gradient of 15% at speeds which resulted in exhaustion after approximately 1 (R_{15%, 1min}) and 2–3 min (R_{15%, 2–3min}), respectively. On the 3rd day, the subjects ran with the treadmill at a gradient of 1% at a speed which caused exhaustion after 2–3 min (R_{1%, 2–3min}). The runner performance was assessed from 400 m [RR, median 64.8 (range 62.2–69.6) s; SMDR, median 49.4 (range 48.5–52.0) s] and 800 m [RR, median 158.8 (range 153.3–170.2) s; SMDR, median 115.2 (range 113.3–123.3) s] track times. Muscle biopsies from gastrocnemius muscle were obtained before and immediately after R_{15%, 2–3min}, from which muscle lactate and creatine phosphate (CP) concentrations, fibre type distribution, capillaries per fibre, total lactate dehydrogenase (LDH) activity and the LDH isoenzyme pattern were determined. The MOD increased with the treadmill gradient and duration. During both treadmill and track runs, SMDR performance was superior to that of RR, but no significant differences were observed with respect to MOD, muscle fibre type distribution, total LDH activity, its iso-enzyme pattern, changes in muscle lactate or CP concentrations. However, after treadmill runs, peak venous lactate concentration and partial pressures of carbon dioxide were higher, and pH lower in SMDR. Also the number of capillaries per muscle fibre and the maximal oxygen uptake were larger in SMDR. These findings would suggest that the superior performance of SMDR depended more on their aerobic than on their anaerobic capacity.     

Alkaloid chemotaxonomy of Nordic Papaver sect. Scapiflora (Papaveraceae)

A chemotaxonomic study of the Nordic Papaver species belonging to the Scapiflora group has been carried out by means of gas chromatography (GC), mass spectro-graphy (MS), and thin layer chromatography (TLC). The data obtained were analysed by the aid of hard and fuzzy clustering. Of the alkaloids identified, protopine and allocryptopine were found in all species investigated (i.e. Papaver radicaium - including all subspecies - P. dahlianum, P. lapponicum , and P. laesiadianum ). Protopine and allocryptopine were the only alkaloids found in P. dahlianum, P. lapponicum , and P. laesiadianum . In addition O -methylthalisopavine was found in all investigated subspecies of P. radicatum; reframine in P. radicatum sspp. ovatilobum, gjaerevollii, groevudalense, intermedium, oeksendalense, radicatum, relictum , and subglobosum; reframidine in ssp. hyperboreum; cryptopine in sspp. ovatilobum, gjaerevollii, groevudalense, relictum, subglobosum, macrostigma , and hyperboreum; muramine in sspp. macrostigma and hyperboreum; and amurine in sspp. relictum and subglobosum .
These chemotaxonomic results confirm the systematics of the Nordic Papavers of the sect. Scapiflora introduced by Knaben who based the taxonomy on morphological and cytological characteristics. Moreover, the content of alkaloids in the different isolated Nordic Papaver populations may be of plant geographical importance. There are, for instance, a marked chemical difference between all the South Norwegian subspecies of P. radicatum and the North Norwegian P. radicatum ssp. subglobosum on one hand and the rest of the North Norwegian subspecies on the other.     

Drosophila melanogaster deoxyribonucleoside kinase activates gemcitabine

Drosophila melanogaster multisubstrate deoxyribonucleoside kinase (Dm-dNK) can additionally sensitize human cancer cell lines towards the anti-cancer drug gemcitabine. We show that this property is based on the Dm-dNK ability to efficiently phosphorylate gemcitabine. The 2.2 Å resolution structure of Dm-dNK in complex with gemcitabine shows that the residues Tyr70 and Arg105 play a crucial role in the firm positioning of gemcitabine by extra interactions made by the fluoride atoms. This explains why gemcitabine is a good substrate for Dm-dNK.